This invention relates generally to support structures for the stationary level mounting of heavy objects such as air conditioner condensers and the like. More specifically the invention relates to support structures particularly well-suited for mounting such objects on inclined surfaces and especially building roof tops.
To take advantage of unused space, air conditioner condensers and other heavy objects such as electrical transformers are frequently mounted on building roof tops. The roof top location also provides excellent air circulation that often aids in the operation of such apparatus.
Because of the difficulties involved in supporting and anchoring these heavy objects, roof top mounting is most frequently done on flat roofed buildings. Roof tops are generally constructed only so as to be able to withstand the forces of winds and snow accumulation. Maximum loading is approximately 150 to 200 pounds per square foot and for this reason substantial support is required to prevent the weight of the objects from damaging the roof top.
For roof mounting heavy objects one means of support frequently used is in the form of a steel frame, generally made from "I" beams or angle iron. The steel frame supports the object on legs that have been securely fastened to the underlying roof support structure, which is usually in the form of wooden roof beams or steel bar joists. The legs are made long enough so that the object is supported above the level of the roof top and the load is transmitted directly to the beams or roof support steel.
The above-described form of support has several disadvantages. The installation of a steel frame is labor intensive and costly from the standpoint of materials. When a heavy object is to be mounted on an existing building, an opening must be made in the roof top to gain access to the underlying roof beams or support steel. The opening must be "framed-off" and well sealed to prevent water leakage into the underlying roof support structure. Also, if reroofing subsequently becomes necessary, it is difficult to refinish the surface underneath the steel structure due to the limited space between it and the roof top.
Another practice of roof mounting heavy objects has been to fabricate a wooden support structure, similar to the steel structure described above. To protect the wood from weather and insects, the exposed portion of the support structure is encased in a metal shroud. Since the wooden support structure must also be anchored to the underlying roof beams or support steel and the metal shroud is subject to corrosion, water leakage is a frequent problem.
A third practice of roof mounting has been to place a molded polyethylene pad on the roof surface and resting the heavy object on the pad. While weather-resistant, the molded polyethylene pad, cannot be readily adapted to meet the individual requirements of each installation. Air conditioner condensers and the like are desirably mounted so as to be horizontally level. Since most flat roofs have some slope (of varying degree) to aid in draining off water, some means of shimming the pad to the level position is required. The molds needed to manufacture the polyethylene pad are not easily retooled to compensate for individual roof slopes.
Molded polyethylene pads have also been used to mount heavy objects at ground level. Again, some means of shimming the pad to the level position is required.
Another practice for mounting heavy objects at ground level has been to fabricate a mounting pad from concrete. The pad must be constructed at the desired location and installation of the object delayed until the concrete has cured, thus necessitating the return of workmen to complete the mounting procedure. Since it is not economically feasible to supply ready-mixed concrete in small quantities several such pads are usually poured from a single truckload of concrete or the concrete is mixed at the mounting site.